Adaptive power control for wireless charging of devices

ABSTRACT

Exemplary embodiments are directed to wireless power transfer. A wireless power transmitter includes a transmit antenna and a controller. The transmit antenna inductively transfers power to a plurality of receiver devices. The controller is operably coupled to the transmit antenna and causes a first one of the plurality of receiver devices to be enabled to receive the power from the transmit antenna and causes at least a portion of the remaining receiver devices to be disabled from receiving the power while the first receiver device is enabled.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/918,365 entitled “ADAPTIVE POWER CONTROL FOR WIRELESS CHARGING OFDEVICES,” filed Jun. 14, 2013, which is a continuation of U.S. patentapplication Ser. No. 12/616,034 entitled “ADAPTIVE POWER CONTROL FORWIRELESS CHARGING,” filed Nov. 10, 2009, which claims benefit under 35U.S.C. §119(e) to: U.S. Provisional Patent Application 61/146,586entitled “POWER SHARING FOR WIRELESS POWER DEVICES” filed on Jan. 22,2009; U.S. Provisional Patent Application 61/151,156 entitled “DYNAMICPOWER CONTROL METHODOLOGY FOR WIRELESS CHARGING” filed on Feb. 9, 2009;and U.S. Provisional Patent Application 61/183,907 entitled “ADAPTIVEPOWER CONTROL FOR WIRELESSLY CHARGING DEVICES” filed on Jun. 3, 2009.The disclosure of all of the priority applications are herebyincorporated by reference in their entirety.

BACKGROUND

Field

The described technology generally relates to wireless charging, andmore specifically to devices, systems, and methods related to allocatingpower to receiver devices that may be located in wireless power systems.

Background

Typically, each battery powered device such as a wireless electronicdevice requires its own charger and power source, which is usually analternating current (AC) power outlet. Such a wired configurationbecomes unwieldy when many devices need charging.

Approaches are being developed that use over-the-air or wireless powertransmission between a transmitter and a receiver coupled to theelectronic device to be charged. Such approaches generally fall into twocategories. One is based on the coupling of plane wave radiation (alsocalled far-field radiation) between a transmit antenna and a receiveantenna on the device to be charged. The receive antenna collects theradiated power and rectifies it for charging the battery. Antennas aregenerally of resonant length in order to improve the couplingefficiency. This approach suffers from the fact that the power couplingfalls off quickly with distance between the antennas, so charging overreasonable distances (e.g., less than 1 to 2 meters) becomes difficult.Additionally, since the transmitting system radiates plane waves,unintentional radiation can interfere with other systems if not properlycontrolled through filtering.

Other approaches to wireless energy transmission techniques are based oninductive coupling between a transmit antenna embedded, for example, ina “charging” mat or surface and a receive antenna (plus a rectifyingcircuit) embedded in the electronic device to be charged. This approachhas the disadvantage that the spacing between transmit and receiveantennas must be very close (e.g., within thousandths of meters). Thoughthis approach does have the capability to simultaneously charge multipledevices in the same area, this area is typically very small and requiresthe user to accurately locate the devices to a specific area.

For many wireless charging systems, the power transmitted from thesource is fixed to a single level, thus the power level generally cannotbe adjusted to accommodate devices with different maximum peak powerlevels. This limits the type of devices that can be charged. Anotherproblem is that fixed radiated power levels cannot be adjusted as afunction of the device's current battery level. This wastes power sinceas the battery charges it needs less and less power to complete thecharge. Radiated power from the transmitter that is not absorbed by thedevice can increase Specific Absorption Rate (SAR) levels. A fixedtransmitter power dictates that SAR requirements must be met for theworst case which occurs when the device being charged has poor couplingto the transmitter. Hence, a device with good coupling is limited to thepower levels dictated by devices with poor coupling, which can lead toincreased charge time for that device. When charging multiple devices, afixed transmit power implies the same power level must be applied to alldevices, no matter what charge level is optimum for each device. Asmentioned earlier, this can result in wasted radiated power.

With wireless power transmission there is a need for apparatuses andmethods for transmitting and relaying wireless power at varying powerlevels and multiplexed times to increase power transmission efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified block diagram of a wireless power transfersystem.

FIG. 2 shows a simplified schematic diagram of a wireless power transfersystem.

FIG. 3 shows a schematic diagram of a loop antenna for use in exemplaryembodiments of the present invention.

FIG. 4 is a simplified block diagram of a transmitter, in accordancewith an exemplary embodiment of the present invention.

FIG. 5 is a simplified block diagram of a receiver, in accordance withan exemplary embodiment of the present invention.

FIG. 6 shows a simplified schematic of a portion of transmit circuitryfor carrying out messaging between a transmitter and a receiver.

FIG. 7 shows a simplified schematic of a portion of the transmitcircuitry for adjusting power levels of a transmitter.

FIG. 8 is a simplified block diagram of an AC-DC power supply that maybe used to supply power to a transmitter.

FIG. 9 illustrates a Pulse Width Modulator (PWM) controller that drivestwo N-channel transistors to create a synchronous buck converter.

FIG. 10 illustrates an exemplary synchronous buck converter using amicrocontroller.

FIG. 11 illustrates a host device with a transmit antenna and includingreceiver devices placed nearby.

FIGS. 12A and 12B are simplified timing diagrams illustrating amessaging protocol for communication between a transmitter and areceiver and for power transmission.

FIG. 13A-13C illustrates a host device with a transmit antenna andincluding receiver devices placed in various positions relative to thetransmit antenna.

FIGS. 14A-14G are simplified timing diagram illustrating adaptive powercontrol for delivering power to multiple receiver devices.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention can be practiced. The term “exemplary”used throughout this description means “serving as an example, instance,or illustration,” and should not necessarily be construed as preferredor advantageous over other exemplary embodiments. The detaileddescription includes specific details for the purpose of providing athorough understanding of the exemplary embodiments of the invention. Itwill be apparent to those skilled in the art that the exemplaryembodiments of the invention may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the novelty of theexemplary embodiments presented herein.

The words “wireless power” is used herein to mean any form of energyassociated with electric fields, magnetic fields, electromagneticfields, or otherwise that is transmitted between from a transmitter to areceiver without the use of physical electromagnetic conductors.

FIG. 1 illustrates a wireless transmission or charging system 100, inaccordance with various exemplary embodiments of the present invention.Input power 102 is provided to a transmitter 104 for generating aradiated field 106 for providing energy transfer. A receiver 108 couplesto the radiated field 106 and generates an output power 110 for storingor consumption by a device (not shown) coupled to the output power 110.Both the transmitter 104 and the receiver 108 are separated by adistance 112. In one exemplary embodiment, transmitter 104 and receiver108 are configured according to a mutual resonant relationship and whenthe resonant frequency of receiver 108 and the resonant frequency oftransmitter 104 are very close, transmission losses between thetransmitter 104 and the receiver 108 are minimal when the receiver 108is located in the “near-field” of the radiated field 106.

Transmitter 104 further includes a transmit antenna 114 for providing ameans for energy transmission and receiver 108 further includes areceive antenna 118 for providing a means for energy reception. Thetransmit and receive antennas are sized according to applications anddevices to be associated therewith. As stated, an efficient energytransfer occurs by coupling a large portion of the energy in thenear-field of the transmitting antenna to a receiving antenna ratherthan propagating most of the energy in an electromagnetic wave to thefar field. When in this near-field a coupling mode may be developedbetween the transmit antenna 114 and the receive antenna 118. The areaaround the antennas 114 and 118 where this near-field coupling may occuris referred to herein as a coupling-mode region.

FIG. 2 shows a simplified schematic diagram of a wireless power transfersystem. The transmitter 104 includes an oscillator 122, a poweramplifier 124 and a filter and matching circuit 126. The oscillator isconfigured to generate a desired frequency, which may be adjusted inresponse to adjustment signal 123. The oscillator signal may beamplified by the power amplifier 124 with an amplification amountresponsive to control signal 125. The filter and matching circuit 126may be included to filter out harmonics or other unwanted frequenciesand match the impedance of the transmitter 104 to the transmit antenna114.

The receiver 108 may include a matching circuit 132 and a rectifier andswitching circuit 134 to generate a DC power output to charge a battery136 as shown in FIG. 2 or power a device coupled to the receiver (notshown). The matching circuit 132 may be included to match the impedanceof the receiver 108 to the receive antenna 118. The receiver 108 andtransmitter 104 may communicate on a separate communication channel 119(e.g., Bluetooth, zigbee, cellular, etc).

As illustrated in FIG. 3, antennas used in exemplary embodiments may beconfigured as a “loop” antenna 150, which may also be referred to hereinas a “magnetic” antenna. Loop antennas may be configured to include anair core or a physical core such as a ferrite core. Air core loopantennas may be more tolerable to extraneous physical devices placed inthe vicinity of the core. Furthermore, an air core loop antenna allowsthe placement of other components within the core area. In addition, anair core loop may more readily enable placement of the receive antenna118 (FIG. 2) within a plane of the transmit antenna 114 (FIG. 2) wherethe coupled-mode region of the transmit antenna 114 (FIG. 2) may be morepowerful.

As stated, efficient transfer of energy between the transmitter 104 andreceiver 108 occurs during matched or nearly matched resonance betweenthe transmitter 104 and the receiver 108. However, even when resonancebetween the transmitter 104 and receiver 108 are not matched, energy maybe transferred at a lower efficiency. Transfer of energy occurs bycoupling energy from the near-field of the transmitting antenna to thereceiving antenna residing in the neighborhood where this near-field isestablished rather than propagating the energy from the transmittingantenna into free space.

The resonant frequency of the loop or magnetic antennas is based on theinductance and capacitance. Inductance in a loop antenna is generallysimply the inductance created by the loop, whereas, capacitance isgenerally added to the loop antenna's inductance to create a resonantstructure at a desired resonant frequency. As a non-limiting example,capacitor 152 and capacitor 154 may be added to the antenna to create aresonant circuit that generates resonant signal 156. Accordingly, forlarger diameter loop antennas, the size of capacitance needed to induceresonance decreases as the diameter or inductance of the loop increases.Furthermore, as the diameter of the loop or magnetic antenna increases,the efficient energy transfer area of the near-field increases. Ofcourse, other resonant circuits are possible. As another non-limitingexample, a capacitor may be placed in parallel between the two terminalsof the loop antenna. In addition, those of ordinary skill in the artwill recognize that for transmit antennas the resonant signal 156 may bean input to the loop antenna 150.

Exemplary embodiments of the invention include coupling power betweentwo antennas that are in the near-fields of each other. As stated, thenear-field is an area around the antenna in which electromagnetic fieldsexist but may not propagate or radiate away from the antenna. They aretypically confined to a volume that is near the physical volume of theantenna. In the exemplary embodiments of the invention, magnetic typeantennas such as single and multi-turn loop antennas are used for bothtransmit (Tx) and receive (Rx) antenna systems since magnetic near-fieldamplitudes tend to be higher for magnetic type antennas in comparison tothe electric near-fields of an electric-type antenna (e.g., a smalldipole). This allows for potentially higher coupling between the pair.Furthermore, “electric” antennas (e.g., dipoles and monopoles) or acombination of magnetic and electric antennas is also contemplated.

The Tx antenna can be operated at a frequency that is low enough andwith an antenna size that is large enough to achieve good coupling(e.g., >−4 dB) to a small Rx antenna at significantly larger distancesthan allowed by far field and inductive approaches mentioned earlier. Ifthe Tx antenna is sized correctly, high coupling levels (e.g., −1 to −4dB) can be achieved when the Rx antenna on a host device is placedwithin a coupling-mode region (i.e., in the near-field) of the driven Txloop antenna.

FIG. 4 is a simplified block diagram of a transmitter 200, in accordancewith an exemplary embodiment of the present invention. The transmitter200 includes transmit circuitry 202 and a transmit antenna 204.Generally, transmit circuitry 202 provides RF power to the transmitantenna 204 by providing an oscillating signal resulting in generationof near-field energy about the transmit antenna 204. By way of example,transmitter 200 may operate at the 13.56 MHz ISM band.

Exemplary transmit circuitry 202 includes a fixed impedance matchingcircuit 206 for matching the impedance of the transmit circuitry 202(e.g., 50 ohms) to the transmit antenna 204 and a low pass filter (LPF)208 configured to reduce harmonic emissions to levels to preventself-jamming of devices coupled to receivers 108 (FIG. 1). Otherexemplary embodiments may include different filter topologies, includingbut not limited to, notch filters that attenuate specific frequencieswhile passing others and may include an adaptive impedance match, thatcan be varied based on measurable transmit metrics, such as output powerto the antenna or DC current draw by the power amplifier. Transmitcircuitry 202 further includes a power amplifier 210 configured to drivean RF signal as determined by an oscillator 212. The transmit circuitrymay be comprised of discrete devices or circuits, or alternately, may becomprised of an integrated assembly. An exemplary RF power output fromtransmit antenna 204 may be on the order of 2.5 to 8.0 Watts.

Transmit circuitry 202 further includes a controller 214 for enablingthe oscillator 212 during transmit phases (or duty cycles) for specificreceivers, for adjusting the frequency of the oscillator, and foradjusting the output power level for implementing a communicationprotocol for interacting with neighboring devices through their attachedreceivers.

The transmit circuitry 202 may further include a load sensing circuit216 for detecting the presence or absence of active receivers in thevicinity of the near-field generated by transmit antenna 204. By way ofexample, a load sensing circuit 216 monitors the current flowing to thepower amplifier 210, which is affected by the presence or absence ofactive receivers in the vicinity of the near-field generated by transmitantenna 204. Detection of changes to the loading on the power amplifier210 are monitored by controller 214 for use in determining whether toenable the oscillator 212 for transmitting energy to communicate with anactive receiver.

Transmit antenna 204 may be implemented as an antenna strip with thethickness, width and metal type selected to keep resistive losses low.In a conventional implementation, the transmit antenna 204 can generallybe configured for association with a larger structure such as a table,mat, lamp or other less portable configuration. Accordingly, thetransmit antenna 204 generally will not need “turns” in order to be of apractical dimension. An exemplary implementation of a transmit antenna204 may be “electrically small” (i.e., fraction of the wavelength) andtuned to resonate at lower usable frequencies by using capacitors todefine the resonant frequency. In an exemplary application where thetransmit antenna 204 may be larger in diameter, or length of side if asquare loop, (e.g., 0.50 meters) relative to the receive antenna, thetransmit antenna 204 will not necessarily need a large number of turnsto obtain a reasonable capacitance.

The transmitter 200 may gather and track information about thewhereabouts and status of receiver devices that may be associated withthe transmitter 200. Thus, the transmitter circuitry 202 may include apresence detector 280, an enclosed detector 290, or a combinationthereof, connected to the controller 214 (also referred to as aprocessor herein). The controller 214 may adjust an amount of powerdelivered by the amplifier 210 in response to presence signals from thepresence detector 280 and the enclosed detector 290. The transmitter mayreceive power through a number of power sources, such as, for example,an AC-DC converter (not shown) to convert conventional AC power presentin a building, a DC-DC converter (not shown) to convert a conventionalDC power source to a voltage suitable for the transmitter 200, ordirectly from a conventional DC power source (not shown).

As a non-limiting example, the presence detector 280 may be a motiondetector utilized to sense the initial presence of a device to becharged that is inserted into the coverage area of the transmitter.After detection, the transmitter may be turned on and the RF powerreceived by the device may be used to toggle a switch on the Rx devicein a pre-determined manner, which in turn results in changes to thedriving point impedance of the transmitter.

As another non-limiting example, the presence detector 280 may be adetector capable of detecting a human, for example, by infrareddetection, motion detection, or other suitable means. In some exemplaryembodiments, there may be regulations limiting the amount of power thata transmit antenna may transmit at a specific frequency. In some cases,these regulations are meant to protect humans from electromagneticradiation. However, there may be environments where transmit antennasare placed in areas not occupied by humans, or occupied infrequently byhumans, such as, for example, garages, factory floors, shops, and thelike. If these environments are free from humans, it may be permissibleto increase the power output of the transmit antennas above the normalpower restrictions regulations. In other words, the controller 214 mayadjust the power output of the transmit antenna 204 to a regulatorylevel or lower in response to human presence and adjust the power outputof the transmit antenna 204 to a level above the regulatory level when ahuman is outside a regulatory distance from the electromagnetic field ofthe transmit antenna 204.

As a non-limiting example, the enclosed detector 290 (may also bereferred to herein as an enclosed compartment detector or an enclosedspace detector) may be a device such as a sense switch for determiningwhen an enclosure is in a closed or open state. When a transmitter is inan enclosure that is in an enclosed state, a power level of thetransmitter may be increased.

In exemplary embodiments, a method by which the transmitter 200 does notremain on indefinitely may be used. In this case, the transmitter 200may be programmed to shut off after a user-determined amount of time.This feature prevents the transmitter 200, notably the power amplifier210, from running long after the wireless devices in its perimeter arefully charged. This event may be due to the failure of the circuit todetect the signal sent from either the repeater or the receive coil thata device is fully charged. To prevent the transmitter 200 fromautomatically shutting down if another device is placed in itsperimeter, the transmitter 200 automatic shut off feature may beactivated only after a set period of lack of motion detected in itsperimeter. The user may be able to determine the inactivity timeinterval, and change it as desired. As a non-limiting example, the timeinterval may be longer than that needed to fully charge a specific typeof wireless device under the assumption of the device being initiallyfully discharged.

FIG. 5 is a simplified block diagram of a receiver 300, in accordancewith an exemplary embodiment of the present invention. The receiver 300includes receive circuitry 302 and a receive antenna 304. Receiver 300further couples to device 350 for providing received power thereto. Itshould be noted that receiver 300 is illustrated as being external todevice 350 but may be integrated into device 350. Generally, energy ispropagated wirelessly to receive antenna 304 and then coupled throughreceive circuitry 302 to device 350.

Receive antenna 304 is tuned to resonate at the same frequency, or nearthe same frequency, as transmit antenna 204 (FIG. 4). Receive antenna304 may be similarly dimensioned with transmit antenna 204 or may bedifferently sized based upon the dimensions of the associated device350. By way of example, device 350 may be a portable electronic devicehaving diametric or length dimension smaller that the diameter of lengthof transmit antenna 204. In such an example, receive antenna 304 may beimplemented as a multi-turn antenna in order to reduce the capacitancevalue of a tuning capacitor (not shown) and increase the receiveantenna's impedance. By way of example, receive antenna 304 may beplaced around the substantial circumference of device 350 in order tomaximize the antenna diameter and reduce the number of loop turns (i.e.,windings) of the receive antenna and the inter-winding capacitance.

Receive circuitry 302 provides an impedance match to the receive antenna304. Receive circuitry 302 includes power conversion circuitry 306 forconverting a received RF energy source into charging power for use bydevice 350. Power conversion circuitry 306 includes an RF-to-DCconverter 308 and may also in include a DC-to-DC converter 310. RF-to-DCconverter 308 rectifies the RF energy signal received at receive antenna304 into a non-alternating power while DC-to-DC converter 310 convertsthe rectified RF energy signal into an energy potential (e.g., voltage)that is compatible with device 350. Various RF-to-DC converters arecontemplated, including partial and full rectifiers, regulators,bridges, doublers, as well as linear and switching converters.

Receive circuitry 302 may further include switching circuitry 312 forconnecting receive antenna 304 to the power conversion circuitry 306 oralternatively for disconnecting the power conversion circuitry 306.Disconnecting receive antenna 304 from power conversion circuitry 306not only suspends charging of device 350, but also changes the “load” as“seen” by the transmitter 200 (FIG. 2).

As disclosed above, transmitter 200 includes load sensing circuit 216which detects fluctuations in the bias current provided to transmitterpower amplifier 210. Accordingly, transmitter 200 has a mechanism fordetermining when receivers are present in the transmitter's near-field.

When multiple receivers 300 are present in a transmitter's near-field,it may be desirable to time-multiplex the loading and unloading of oneor more receivers to enable other receivers to more efficiently coupleto the transmitter. A receiver may also be cloaked in order to eliminatecoupling to other nearby receivers or to reduce loading on nearbytransmitters. This “unloading” of a receiver is also known herein as a“cloaking.” Furthermore, this switching between unloading and loadingcontrolled by receiver 300 and detected by transmitter 200 provides acommunication mechanism from receiver 300 to transmitter 200 as isexplained more fully below. Additionally, a protocol can be associatedwith the switching which enables the sending of a message from receiver300 to transmitter 200. By way of example, a switching speed may be onthe order of 100 μsec.

In an exemplary embodiment, communication between the transmitter andthe receiver refers to a device sensing and charging control mechanism,rather than conventional two-way communication. In other words, thetransmitter uses on/off keying of the transmitted signal to adjustwhether energy is available in the near-field. The receivers interpretthese changes in energy as a message from the transmitter. From thereceiver side, the receiver uses tuning and de-tuning of the receiveantenna to adjust how much power is being accepted from the near-field.The transmitter can detect this difference in power used from thenear-field and interpret these changes as a message from the receiver.

Receive circuitry 302 may further include signaling detector and beaconcircuitry 314 used to identify received energy fluctuations, which maycorrespond to informational signaling from the transmitter to thereceiver. Furthermore, signaling and beacon circuitry 314 may also beused to detect the transmission of a reduced RF signal energy (i.e., abeacon signal) and to rectify the reduced RF signal energy into anominal power for awakening either un-powered or power-depleted circuitswithin receive circuitry 302 in order to configure receive circuitry 302for wireless charging.

Receive circuitry 302 further includes processor 316 for coordinatingthe processes of receiver 300 described herein including the control ofswitching circuitry 312 described herein. Cloaking of receiver 300 mayalso occur upon the occurrence of other events including detection of anexternal wired charging source (e.g., wall/USB power) providing chargingpower to device 350. Processor 316, in addition to controlling thecloaking of the receiver, may also monitor beacon circuitry 314 todetermine a beacon state and extract messages sent from the transmitter.Processor 316 may also adjust DC-to-DC converter 310 for improvedperformance.

In some exemplary embodiments, the receive circuitry 320 may signal apower requirement, as explained more fully below to a transmitter in theform of, for example, desired power level, maximum power level, desiredcurrent level, maximum current level, desired voltage level, and maximumvoltage level. Based on these levels, and the actual amount of powerreceived from the transmitter, the processor 316 may adjust theoperation of the DC-DC converter 310 to regulate its output in the formof adjusting the current level, adjusting the voltage level, or acombination thereof

FIG. 6 shows a simplified schematic of a portion of transmit circuitryfor carrying out messaging between a transmitter and a receiver. In someexemplary embodiments of the present invention, a means forcommunication may be enabled between the transmitter and the receiver.In FIG. 6 a power amplifier 210 drives the transmit antenna 204 togenerate the radiated field. The power amplifier is driven by a carriersignal 220 that is oscillating at a desired frequency for the transmitantenna 204. A transmit modulation signal 224 is used to control theoutput of the power amplifier 210.

The transmit circuitry can send signals to receivers by using an ON/OFFkeying process on the power amplifier 210. In other words, when thetransmit modulation signal 224 is asserted, the power amplifier 210 willdrive the frequency of the carrier signal 220 out on the transmitantenna 204. When the transmit modulation signal 224 is negated, thepower amplifier will not drive out any frequency on the transmit antenna204.

The transmit circuitry of FIG. 6 also includes a load sensing circuit216 that supplies power to the power amplifier 210 and generates areceive signal 235 output. In the load sensing circuit 216 a voltagedrop across resistor R_(s) develops between the power in signal 226 andthe power supply 228 to the power amplifier 210. Any change in the powerconsumed by the power amplifier 210 will cause a change in the voltagedrop that will be amplified by differential amplifier 230. When thetransmit antenna is in coupled mode with a receive antenna in a receiver(not shown in FIG. 6) the amount of current drawn by the power amplifier210 will change. In other words, if no coupled mode resonance exist forthe transmit antenna 210, the power required to drive the radiated fieldwill be a first amount. If a coupled mode resonance exists, the amountof power consumed by the power amplifier 210 will go up because much ofthe power is being coupled into the receive antenna. Thus, the receivesignal 235 can indicate the presence of a receive antenna coupled to thetransmit antenna 235 and can also detect signals sent from the receiveantenna. Additionally, a change in receiver current draw will beobservable in the transmitter's power amplifier current draw, and thischange can be used to detect signals from the receive antennas.

Details of some exemplary embodiments for cloaking signals, beaconsignals, and circuits for generating these signals can be seen in U.S.Utility patent application Ser. No. 12/249,873, entitled “REVERSE LINKSIGNALING VIA RECEIVE ANTENNA IMPEDANCE MODULATION” filed on Oct. 10,2008; and in U.S. Utility patent application Ser. No. 12/249,861,entitled “TRANSMIT POWER CONTROL FOR A WIRELESS CHARGING SYSTEM” filedon Oct. 10, 2008, both herein incorporated by reference in theirentirety.

Details of exemplary communication mechanisms and protocols can be seenin U.S. Utility patent application Ser. No. 12/249,866 entitled“SIGNALING CHARGING IN WIRELESS POWER ENVIRONMENT” filed on Oct. 10,2008, the contents of which is incorporated by reference herein in itsentirety.

FIG. 7 shows a simplified schematic of a portion of the transmitcircuitry for adjusting power levels of a transmitter. In some exemplaryembodiments, the controller 214 may be coupled to a voltage regulator240, a current limiter 242, or a combination thereof to control theamount of power delivered on the power in signal 226 relative to thesupplied DC in 415. In addition, some exemplary embodiments may includea current detector 252 and a voltage detector 250 coupled to the powerin signal 226 and used to provide feedback to the controller regardingthe consumption of power. The load sensing circuit 216 of FIG. 6 is oneexample of a suitable current detector.

As stated earlier with reference to FIGS. 1, 2, and 4, power may bedelivered, using the transmit circuitry 202 and transmit antenna 204, toreceiver devices needing charge by placing the receiver devices in thevicinity of a coupling-mode region of the transmit antenna. In exemplaryembodiments discussed herein, the transmitter can cycle powersequentially to all of the receiver devices to be charged based on powerlevel, time, and the like. Receiver devices may communicate device powerrequirements and other information to the transmitter. With this powerrequirement information, the transmitter can tailor the amount of powerthat is delivered to each receiver device by adjusting the amount ofpower transmitted, adjusting the amount of time that power istransmitted, or a combination thereof.

Combinations of the voltage regulator 240 and the current limiter 242may be used to implement the proper circuitry for adjusting power levelsof the transmitter. An adjustable voltage regulator circuit may, forexample, include an adjustable potentiometer, a rectifier, possibly asmoothing circuit and possibly a band-gap reference circuit. Example ofsome voltage regulator circuits suitable for use with embodiments of theinvention are illustrated and discussed with reference to FIGS. 8, 9,and 10 below.

A receiver device requiring charging may signal its power requirementneeds, for example, in terms of current and voltage to the transmitter.For example, a protocol may be included wherein each receiver devicewanting charging signals its power ratings including its peak voltageand current levels. Additionally, a recommended level of current andvoltage may also be signaled. Further, an identifier for each device tobe charged can likewise be signaled.

The processor 214 may then control, for example, the power that isdelivered to the power amplifier 210 (FIG. 6) through the power insignal 226.

In some exemplary embodiments, a voltage detector 250 may be included,for example, either separately as shown in FIG. 7 or as part of thevoltage regulator 240. The voltage detector 250 forms a feedback pathwith the controller 214 to adjust power levels on the power in signal226. Thus, in connection with controlling the current, the controller214 may adjust a level within the voltage regulator 240 within specifiedlimits to provide optimal charging to a device to be charged. Thus, thatoptimal level may be set to not exceed the power rating of the device asdetermined by the fact that power is the product of voltage and current.

In some exemplary embodiments, a current detector 252 may be included,for example, either separately as shown in FIG. 7 or as part of thecurrent regulator 242. The voltage detector 250 forms a feedback pathwith the controller 214 to adjust power levels on the power in signal226. Thus, in connection with controlling the voltage, the controller214 may adjust a level within the current limiter 242 within specifiedlimits to provide optimal charging to a device to be charged. Thus, theoptimal level may be set to not exceed the power rating of the device asdetermined by the fact that power is the product of voltage and current.

With the current detector 252 and voltage detector 250, the power drawnby each receiver device may be monitored in connection with the voltageand current detectors providing power component (voltage or current)threshold detection. Thus, the controller 214 may adjust voltage andcurrent to different levels for each receiver device that is beingcharged throughout a charging process.

The receiver devices may signal power requirement needs via a wirelesscharging signaling protocol as discussed above. In addition, a separatecommunication channel 119 (e.g., Bluetooth, zigbee, cellular, etc.) maybe used to signal power requirements.

Exemplary embodiments of the invention are directed to a dynamictransmit radiated power level control by utilizing adaptive control ofthe drive voltage, drive current, or a combination thereof to drive thepower amplifier 210 (FIG. 6). Changing the drive level changes the RFpower output from the PA and hence the power transmitted to the receivedevices being charged.

Some exemplary information used to define power levels may include:

1—the device type and optimum RF power level the receiver device wouldlike to see,

2—the current battery charge level of the device being charged, and

3—the RF power level from the transmit source that each device iscurrently receiving.

Knowing the device type and its preferred RF power level for charging(item 1), the transmit source can be adjusted to this level during thetime slot over which it is getting charged, as explained more fullybelow. Thus, the power level delivered to each device can beindependently customized for that device without impacting any of theother devices. Additionally, knowledge of the current battery chargelevels of a device being charged (item 2) allows for the radiated RFlevel to be optimized based on the current battery charge level of thedevice. Both techniques help to minimize power that would normally bewasted if a fixed transmit power level were implemented.

In addressing RF safety issues, comparing the power level absorbed byeach device (item 3) to the power transmitted from the transmitter givesan indication of the total power radiated to the local environment whichin turn is proportional to the transmitter SAR level. This allows ameans to maximize the radiated power to each device based on eachdevice's coupling ratios to the transmitter while still maintainingacceptable SAR levels. As a result, one is able to improve the powerdelivered to each device individually rather than be limited to a lowerfixed power level dictated by the device with poor coupling to thetransmitter. Finally, adjustable radiated power allows for a lower powerbeacon mode that reduces transmitter AC power consumption when not incharging mode and also reduces the interference to locally-situatedelectronics.

FIGS. 8, 9, and 10 illustrate exemplary circuitry that may be used toregulate and adjust power levels for the power amplifier 210 and othertransmit circuitry 202. In FIG. 8, an AC-DC power supply 400 converts120 volts AC 405 to the various DC voltages that may be required by thetransmitter, such as, for example, 5 volt and 100 mA auxiliary power torun the transmit circuitry 202 and 5-12 volt and 500 mA main power torun the power amplifier 210, which drives the transmit antenna 204.

An AC-DC converter 410 generates an intermediate DC voltage 415 (alsoreferred to herein as “DC in”) for a circuitry regulator 420 and a PAregulator 450. The circuitry regulator 420 provides general power 425for the transmit circuitry 202 and the PA regulator provides variablepower levels for the power in signal 226 to drive the PA 210.

The AC-DC converter 410 may be, for example, a conventional “wall wart”that allows an Underwriter Laboratories (UL) and Canadian StandardsAssociation (CSA) approved power supply to be the “certified” section ofthe system while keeping costs down. Quasi-regulated (e.g., about 10%)wall warts are inexpensive and are available from a wide variety ofvendors.

As non-limiting examples, the circuitry regulator 420 and a PA regulator450 may be implemented as buck voltage converters. The dual buck designof a circuitry regulator 420 and a PA regulator 450 may keepefficiencies high, at the expense of additional switch-mode controllers,Field Effect Transistors (FETs), capacitors, and inductors.

Thus, the circuitry regulator 420 may be a low-power fixed-output buckconverter that provides 5 volts for the controller 214 and othercircuitry as illustrated in FIG. 4. The PA regulator 450 may be a higherpower variable-output buck converter that supplies a varying voltage tothe power amplifier to control the power output of the transmitter. Thepower amplifier supply 226 is controllable by a control signal 452 fromthe transmit circuitry 202 to the PA regulator 450, which varies thetransmitted RF power over, for example, a range of about 50 mW to about5 watts.

FIG. 9 illustrates a PA regulator 450A implemented as a Pulse WidthModulator (PWM) controller 460 (such as a Linear Technology LTC3851)that drives two N-channel transistors to comprise a synchronous buckconverter. A small inductor, a resistor ladder, and an output capacitorfilter the output of the transistors to complete the buck converter. Thebuck converter converts and regulates the DC in voltage 415 to a DC outvoltage 226.

Power output may be controlled, for example, by a digital (programmable)potentiometer 465 controlled by the control signal 452. The controlsignal 452 may be driven by the controller 214 (FIG. 4) such that the DCout voltage 226 can be set anywhere from, for example, 5 to 12 volts DC.PA regulator 450A takes very little controller overhead, and may beconfigured to have guaranteed loop stability under conditions of rapidlychanging load with over 90% efficiency.

Alternatively, FIG. 10 illustrates a PA regulator 450B as a synchronousbuck converter using a microcontroller 470. The microcontroller 470 maybe dedicated to the synchronous buck converter function. However, insome exemplary embodiments, the controller 214 of the transmitter 200(FIG. 4) may be used for the synchronous buck converter function as wellas the other functions that it is performing. The buck converterconverts and regulates the DC in voltage 415 to a DC out voltage 226.

Thus, the microcontroller 470 may directly drive a P-channel and anN-channel FET to provide the switch control for the buck converter. Asmall inductor, a resistor ladder, and an output capacitor filter theoutput of the transistors to complete the buck converter. Feedback maybe directly into an A/D input of the microcontroller 470 as a voltagesensing operation. Thus, the control signal 452 may be embodied as asampled version of the voltage on DC out 226. The microcontroller 470may compare actual output on DC out 226 to desired output and correctthe PWM signal accordingly. Since frequencies may be much lower for amicrocontroller 470 implementation, a larger inductor may be required,which is not a big problem in the transmitter. A microcontroller 470implementation may be considerably cheaper, since no separate PWMcontroller is required.

As stated above, benefits to allowing for dynamically adjustabletransmit power are:

1—customization of the power delivered to individual device typesthereby allowing for more device types to be charged with a singlecharger design;

2—avoidance of wasted radiated power by allowing for varying powerlevels to be delivered to multiple devices as a function of currentbattery charge level in a way that doesn't impact charge times of otherdevices;

3—improved charge times by allowing for radiated power levels based onthe individual device's coupling levels to the transmitter in a mannerthat still meets SAR requirements; and

4—reduced power consumption when the charger is not charging a device(beacon mode) and reduced interference to nearby electronics.

FIG. 11 illustrates a host device 510 with transmit circuitry 202 and atransmit antenna 204. Receiver devices 520 are shown placed within thecoupling-mode region of the transmit antenna 204. Although notillustrated, the receiver devices may include receive antennas 304 andreceive circuitry 302 as shown in FIG. 5. In FIG. 11, the host device410 is illustrated as a charging mat, but could be integrated intofurniture or building elements such as walls, ceilings, and floors.Furthermore, the host device 510 may be an item such as, for example, ahandbag, backpack, or briefcase with a transmitter built in.Alternatively, the host device may be a portable transmitterspecifically designed for a user to transport and charge receiverdevices 520, such as a charging bag.

“Coplanar,” as used herein, means that the transmit antenna and receiveantenna have planes that are substantially aligned (i.e., have surfacenormals pointing in substantially the same direction) and with nodistance (or a small distance) between the planes of the transmitantenna and the receive antenna. “Coaxial,” as used herein, means thatthe transmit antenna and receive antenna have planes that aresubstantially aligned (i.e., have surface normals pointing insubstantially the same direction) and the distance between the twoplanes is not trivial and furthermore, the surface normal of thetransmit antenna and the receive antenna lie substantially along thesame vector, or the two normals are in echelon.

Coplanar placements may have relatively high coupling efficiencies.However, coupling may vary depending on where the receive antennas areplaced relative to the transmit antenna. For example, a coplanarplacement point outside of the transmit loop antenna may not couple asefficiently as a coplanar placement point inside the transmit loop.Furthermore, coplanar placement points within the transmit loop, but atdifferent locations relative to the loop, may have different couplingefficiencies.

Coaxial placements may have lower coupling efficiencies. However,coupling efficiencies may be improved with the used of repeaterantennas, such as are described in U.S. Utility patent application Ser.No. 12/249,875 entitled “METHOD AND APPARATUS FOR AN ENLARGED WIRELESSCHARGING AREA” filed on Oct. 10, 2008, the contents of which isincorporated by reference herein in its entirety.

FIG. 12A is a simplified timing diagram illustrating an exemplarymessaging protocol for communication between a transmitter and areceiver using the signaling techniques discussed above. In oneexemplary approach, signals from the transmitter to the receiver arereferred to herein as a “forward link” and use a simple AM modulationbetween normal power transmission and lower power transmission. Othermodulation techniques are also contemplated. As a non-limiting example,a signal present may be interpreted as a “1” and no signal present maybe interpreted as a “0” (i.e., on-off keying).

Reverse link signaling is provided by modulation of power drawn by thereceive device, which can be detected by the load sensing circuit in thetransmitter. As a non-limiting example, higher power states may beinterpreted as a 1 and lower power states may be interpreted as a 0. Itshould be noted that the transmitter must be on for the receiver to beable to perform the reverse link signaling. In addition, the receivershould not perform reverse link signaling during forward link signaling.Furthermore, if two receive devices attempt to perform reverse linksignaling at the same time a collision may occur, which will make itdifficult, if not impossible for the transmitter to decode a properreverse link signal.

FIG. 12A illustrates a simple and low power form of the messagingprotocol. A synchronization pulse 620 is repeated every recurring period610 (about one second in the exemplary embodiment) to define thebeginning of the recurring period. As a non-limiting example, the syncpulse on time may be about 40 mS. The recurring period 610, with atleast a synchronization pulse 620, may be repeated indefinitely whilethe transmitter is on. Note that “synchronization pulse” is somewhat ofa misnomer because the synchronization pulse 620 may be a steadyfrequency during the pulse period 620. The synchronization pulse 620 mayalso include signaling at the resonant frequency with the ON/OFF keyingdiscussed above and as illustrated by the “hatched” pulse 620. FIG. 12Aillustrates a minimal power state wherein power at the resonantfrequency is supplied during the synchronization pulse 420 and thetransmit antenna is off during a power period 650. All receiver devicesare allowed to receive power during the synchronization pulse 420.

FIG. 12B illustrates the recurring period 610 with a synchronizationpulse 620, a reverse link period 630 and a power period 650′ wherein thetransmit antenna is on and supplying full power by oscillating at theresonant frequency and not performing any signaling. The power period450′ may be segmented into different periods for multiple receiverdevices as is explained below. FIG. 12B shows three power segments Pd1,Pd2, and Pdn for three different receiver devices.

The on-off keying communication protocol discussed above may be expandedto enable each receiver device to request charge and indicate desiredpower parameters as discussed above. In addition, a receiver device mayidentify itself with a unique identifier, such as, for example a serialnumber or a tag associating the receiver device with a specific user.The requesting receiver device may also communicate additionalinformation such as class of device (e.g., camera, cell phone, mediaplayer, personal digital assistant).

Receiver information may include items such as; unique deviceidentifiers, device types, contact information, and user-programmedinformation about the device. For example, the device may be a musicplayer, from a specific manufacturer, that is tagged with a user's name.As another example, the device may be an electronic book, from aspecific manufacturer, with a specific serial number that is tagged witha user's name.

In addition to communication using the on-off keying communicationprotocol discussed above, the receiver and transmitter may communicateon a separate communication channel 119 (e.g., Bluetooth, zigbee,cellular, etc.). With a separate communication channel, the recurringperiod need not include any communication periods and the entire timemay be devoted to the power period 650′. The transmitter may stillallocate time slots to each receiver device (communicated over theseparate communication channel) and each receiver device only gets onthe bus for its allocated power segment Pdn.

As described above, it may be important in many applications to be ableto allocate a certain percentage of power between each of the poweredreceiver devices, so that each receiver device is powered appropriately.In some cases this will be an even division of power between allreceiver devices. In other cases, one receiver device may need morepower, perhaps due to a higher power task it must perform periodically.In yet other cases, one receiver device may need less power, perhaps dueto a battery being fully charged. In such a case, the system may want todistribute that receiver device's power allocation to other devices.

There are a number of approaches to power sharing. One simple way is tohave all receiver devices receiving power at the same time, thus sharingthe power available in the wireless power environment. This method issimple, inexpensive and robust, but it may have a drawback that in manyRF/inductive charging environments, one receiver device may couple tothe transmit antenna better than another receiver device. As a result,the first receiver device may get most of the power. Another drawback isthat there is no way to “throttle back” power to a receiver device thathas a fully charged battery.

Another way to allocate power between multiple receiver devices is timedivision multiplexing, where one receiver device at a time is enabled toreceive power. All receiver devices not receiving power are disabledfrom receiving power so that they do not interact with the RF/inductiveenvironment. Time division multiplexing requires a controller that canapportion power between several powered devices, and can optionally makedecisions on unequal allocations of power. As a non-limiting example atransmitter may reduce the length of, or eliminate, the power segment toa device that is fully charged. Time division multiplexing may have thedrawback of losing some efficiency, since summing the couplingefficiency of all receiver devices receiving simultaneously may notequal the efficiency of each receiver device receiving powersequentially. In addition, a receiver device that is off may have tostore power for a long time until its next on period, thus requiring alarger/more expensive charge storage device.

Exemplary embodiments of the disclosure are directed to a hybridtechnique. In an exemplary embodiment of the disclosure, a number ofreceiver devices share a wireless charging area. Initially, they may allshare receive power simultaneously. After some time, a control system,which includes feedback from the receiver devices, notes how much powereach receiver device is actually receiving, and if needed, adjusts powervia a time division multiplexing approach, a power level adjustmentapproach, or a combination thereof. In most cases, each receiver devicewill receive power for most of the time. At some point in time, somereceiver devices may be turned off or disabled from receiving power toreduce their total power received. For example, a receiver device thatis placed on the transmit coil so that it receives most of the powermight be turned off for part of the time so that other receiver devicesreceive more power. As a result, the imbalance caused by the placementof various receiver devices may be corrected. Another example might betwo receiver devices that are placed so they both share power, andinitially both are on 100% of the time. As one device finishes chargingits battery, it could begin to turn itself off for a larger and largerpercentage of the time to allow more power to reach the other device.Alternatively, the transmitter could begin allocating a smaller andsmaller time slot for the almost charged receiver device to allow morepower to reach the other receiver devices.

FIG. 13A-13C illustrates a host device 150 with a transmit antenna 204and including receiver devices (Dev1 and Dev2) placed in variouspositions relative to the transmit antenna 204. For simplicity, only tworeceiver devices are discussed herein but use of multiple devices isalso contemplated to be within the scope of the teachings of thedisclosure and modification for such would be apparent to a person ofordinary skill in the art.

FIG. 13A illustrates a scenario where both receiver devices (Dev1 andDev2) are positioned to receive substantially equal amounts of powerfrom the transmit antenna 204, such as by being about the same distanceaway from the perimeter of the transmit antenna. In FIG. 13A receiverdevices Dev1 and Dev2 are both placed near the center of the transmitantenna 204.

In FIG. 13B, the receiver devices Dev1 and Dev2 are placed away fromeach other but about the same distance from the perimeter of thetransmit antenna 204. Thus, the receiver devices Dev1 and Dev2 do nothave to be near each other or in the same geographical location withinthe powering region to receive the same amount of power from thetransmit antenna 204. It should be noted that due to the varyingcoupling efficiencies associated with a device's distance from atransmitter, in a FIG. 13A setting, the receiver devices Dev1 and Dev2may receive less power from the transmit antenna 204 than in a FIG. 4Bsetting. However, in each setting the amount of power received in one ofthe devices is substantially equal to the amount of power received inthe other device.

FIG. 13C illustrates a scenario wherein the receiver devices Dev1 andDev2 are positioned to receive unequal amount of power from the transmitantenna 204. In this example, receiver device Dev1 is placed near thecenter of the transmit antenna 204, and will likely receive less powerthan receiver device Dev2 placed closer to the transmit antenna 204. Inthis scenario, Dev2 would charge faster than Dev1 and therefore becomefully charged sooner than Dev1.

FIGS. 14A-14G are simplified timing diagram illustrating adaptive powercontrol for delivering power to multiple receiver devices. Forsimplicity, only two devices are discussed herein but use of multipledevices is also contemplated to be within the scope of the teachings ofthe disclosure and modification for such would be apparent to a personof ordinary skill in the art.

In FIG. 14A, a case 0 scenario shows a time line 700 to illustrate whena single receiver device is placed within the powering region of thetransmitter antenna 204. In this scenario, the single receiver devicereceives substantially all of the power provided by the transmit antenna204 during each recurring period 610. As discussed above with referenceto FIGS. 12A and 12B, a portion 620 of the recurring period 610 maybespent on optional signaling.

In FIG. 14B, a case 1 scenario shows a time line 711 for receiver deviceDev1 and a time line 712 for receiver device. Dev2. In this case, eachreceiver device Dev1 and Dev2 is consuming about 50% of the powersupplied by the transmit antenna 204. Scenario 14B is likely when thetwo receiver devices are positioned symmetrically within a poweringregion of the transmit antenna 204, such as in FIGS. 13A and 13B. Thus,each of the receiver devices Dev1 and Dev2 receive an equal amount ofpower during the recurring period 610, such as receiving 50% of thepower as shown by the vertical axis. Signaling periods 620 may also beused to allow communication between transmitter and receiver, and mayreduce the charging time available for both devices.

In FIG. 14C, a case 2 scenario, illustrated by times lines 721 and 722,uses time multiplexing. Thus, each of the receiver devices Dev1 and Dev2receives an equal amount of power during the recurring period 610.However, in case 2, Dev1 is enabled to receive 100% of the power for 50%of the recurring period 610, and Dev2 is enabled to receive 100% of thepower for the other 50% of the recurring period 610. Signaling periods620 may also be used to allow communication between transmitter andreceiver, and may reduce the charging time available for both devices.

In FIG. 14D, a case 3 scenario illustrates times lines 731 and 732,wherein both receiver devices Dev1 and Dev2 may be enabled to receivepower during the signaling periods 610. Even though signaling may beoccurring, the receiver devices Dev1 and Dev2 can still extract powerfrom the signal. Thus, in case 3 each of the receive devices is enabledto receive power during the signaling periods 620 and thus receive about50% of the power during the signaling periods 620. The power portion ofthe recurring period 610 (i.e., the portion of the recurring period 610not used by the signaling period 620) may be equally split to timedivision multiplex between receiver device Dev1 and receiver deviceDev2.

In FIG. 14E, a case 4 scenario shows a time line 741 for receiver deviceDev1 and a time line 742 for receiver device Dev2. In case 4, thereceiver devices Dev1 and Dev2 are positioned to receive unequal amountof power from the transmit antenna 204, such as receiver device Dev1placed near the center of the transmit antenna 204 and receiving lesspower than receiver device Dev2 placed closer to the transmit antenna204 (as shown in FIG. 13C). Each of receiver devices Dev1 and Dev2 relyon their coupling to the transmit antenna 204 to apportion the powerbetween the two devices in the powering region. Thus, in case 4, abetter positioned receiver device, such as receiver device Dev2,receives about 75% of the power while receiver device Dev1 receives theother 25% of the power, since power division is sub-optimally determinedpurely by position relative to the transmit antenna 204.

In FIG. 14F, a case 5 scenario shows a time line 751 for receiver deviceDev1 and a time line 752 for receiver device Dev2. In case 5, thereceiver devices Dev1 and Dev2 are positioned to receive unequal amountof power from the transmit antenna in a similar manner to that of FIG.14E. However, while each receiver device relies partly upon its relativecoupling to the transmit antenna 204 to apportion power, each receiverdevice can also decouple itself from the transmit antenna 204 if needed.If a 50/50 power split is desired, receiver device Dev2 can disableitself from receiving power for a P2 portion of the recurring period610, while Dev1 remains enabled to receive 100% of the power during theP1 portion.

During the P1 portion and the signaling portion 620 both receiverdevices remain on such that receiver device Dev1 receives about 25% ofthe power and receiver device Dev2 receives about 75% of the power. Thelengths of the P1 portion and P2 portion may be adjusted such that about50% of the power (or other apportionment, if desired) is allocated toeach receiver device Dev1 and Dev2. Case 5 is similar to case 2, butrequires less off-time. For example in case 5 receive device Dev1 isnever turned disabled from receiving power and just receives more powerduring the P2 portion due to receiver device Dev2 being disabled.

In FIG. 14G, a case 6 scenario shows a time line 761 for receiver deviceDev1 and a time line 762 for receiver device Dev2. Recall from thediscussion above with respect to FIGS. 7-10, that the power output ofthe transmit antenna 204 may be adjusted. Thus, in FIG. 14G power outputis shown in terms of Watts, rather than in terms of percentage of fullpower. In case 6, receiver devices Dev1 and Dev2 are positioned toreceive about equal amounts of power from the transmit antenna 204.Thus, during the signaling period 620 the transmitter may be set todeliver about 4 Watts and each of receiver devices Dev1 and Dev2 mayreceive about 2 Watts. During the P1 portion, receiver device Dev1 isdisabled from receiving power and the power output of the transmitantenna is set to about 3 Watts, which is mostly consumed by receiverdevice Dev2. During the P2 portion, receiver device Dev2 is disabledfrom receiving power and the power output of the transmit antenna is setto about 4 Watts, which is mostly consumed by receiver device Dev1.

FIGS. 14A-G are given as examples of some possible scenarios. A personof ordinary skill in the art would recognize that many other scenariosinvolving more receiver devices and various power output levels arecontemplated within the scope of the invention.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the exemplary embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the exemplary embodiments of the invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the exemplary embodiments disclosed herein may beimplemented or performed with a general purpose processor, a DigitalSignal Processor (DSP), an Application Specific Integrated Circuit(ASIC), a Field Programmable Gate Array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theexemplary embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module may reside in Random AccessMemory (RAM), flash memory, Read Only Memory (ROM), ElectricallyProgrammable ROM (EPROM), Electrically Erasable Programmable ROM(EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any otherform of storage medium known in the art. An exemplary storage medium iscoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium may be integral to the processor. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosed exemplary embodiments isprovided to enable any person skilled in the art to make or use thepresent invention. Various modifications to these exemplary embodimentswill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other embodiments withoutdeparting from the spirit or scope of the invention. Thus, the presentinvention is not intended to be limited to the embodiments shown hereinbut is to be accorded the widest scope consistent with the principlesand novel features disclosed herein.

What is claimed is:
 1. A wireless power transmitter, comprising: asingle transmit antenna configured to inductively transfer power to aplurality of receiver devices via a magnetic field; and a controlleroperably coupled to the single transmit antenna and configured todetermine an allocation of power to be received from the single transmitantenna by a first and a second one of the plurality of receiver devicesand to cause the first or second receiver devices to enable itselfthemselves, based on the determined allocation of power, to receive theallocation of power from the single transmit antenna and to cause atleast a portion of the remaining receiver devices to disable themselvesfrom receiving the power while the first or second receiver devices areenabled.
 2. The wireless power transmitter of claim 1, wherein thecontroller is configured to cause the first receiver device to enableitself and cause the at least portion of the remaining receiver devicesto disable themselves based on a message sent to the plurality ofreceiver devices.
 3. The wireless power transmitter of claim 2, whereinthe controller is further configured to send the message to theplurality of receiver devices via the magnetic field using an on/offkeying communication protocol or via a separate communication channel.4. The wireless power transmitter of claim 3, wherein the separatecommunication channel comprises Bluetooth, Zigbee or cellular network.5. The wireless power transmitter of claim 1, wherein the controller isfurther configured to adjust the amount of time during which the firstreceiver device is enabled based on a charging level of the firstreceiver device.
 6. The wireless power transmitter of claim 5, whereinthe controller is further configured to cause the first receiver deviceto disable itself from receiving the power when the first receiverdevice has been substantially fully charged with the received power. 7.The wireless power transmitter of claim 6, wherein the controller isfurther configured to cause a second one of the plurality of receiverdevices to enable itself to receive the power from the transmit antennaand cause at least a portion of the remaining receiver devices todisable themselves from receiving the power while the second receiverdevice is enabled.
 8. The wireless power transmitter of claim 1, whereinthe controller is further configured to sequentially cause the pluralityof receiver devices to enable themselves to receive the power andsubstantially equally apportion the amount of time during which each ofthe receiver devices is enabled.
 9. The wireless power transmitter ofclaim 1, wherein the controller is further configured to sequentiallycause the plurality of receiver devices to enable themselves to receivethe power and unequally apportion the amount of time during which eachof the receiver devices is enabled.
 10. A method of wirelesslytransferring power, comprising: inductively transferring power from asingle transmitter to a plurality of receiver devices via a magneticfield; determine an allocation of power to be received from the singletransmitter by a first and a second one of the plurality of receiverdevices; causing, based on the determined allocation of power, the firstor second receiver devices to enable themselves to receive theallocation of power; and causing at least a portion of the remainingreceiver devices to disable themselves from receiving the power whilethe first or second receiver devices are enabled.
 11. The method ofclaim 10, further comprising sending a message to the plurality ofreceiver devices, wherein the causing is performed based on the message.12. The method of claim 11, wherein the message is sent to the pluralityof receiver devices via the magnetic field using an on/off keyingcommunication protocol or via a separate communication channel, andwherein the separate communication channel comprises Bluetooth, Zigbeeor cellular network.
 13. The method of claim 10, further comprisingadjusting the amount of time during which the first receiver device isenabled based on a charging level of the first receiver device.
 14. Themethod of claim 13, further comprising: causing the first receiverdevice to disable itself from receiving the power when the firstreceiver device has been substantially fully charged; and causing thesecond one of the plurality of receiver devices to enable itself toreceive the power from the transmit antenna and causing the at leastportion of the remaining receiver devices to disable themselves fromreceiving the power while the second receiver device is enabled.
 15. Themethod of claim 10, wherein the plurality of receiver devices aresequentially caused to enable themselves and are substantially equallyapportioned with respect to the amount of time during which each of thereceiver devices is enabled.
 16. The method of claim 10, wherein theplurality of receiver devices are sequentially caused to enablethemselves and are unequally apportioned with respect to the amount oftime during which each of the receiver devices is enabled.
 17. Awireless power receiver, comprising: a receive antenna configured toinductively receive power via a magnetic field from a transmitter whichis configured to inductively transfer the power to a plurality ofreceiver devices spaced apart from the receive antenna; and a controlleroperably coupled to the receive antenna and configured to load andunload the receive antenna in order to change the power received via themagnetic field, indicating an amount of power accepted by the receiver,and to cause the receive antenna to enable itself to receive the amountof power from the transmitter while at least a portion of the pluralityof receiver devices is disabled from receiving the power from thetransmitter.
 18. The wireless power receiver of claim 17, wherein thecontroller is configured to cause the receive antenna to enable itselfbased on a message received from the transmitter.
 19. The wireless powerreceiver of claim 18, wherein the receive antenna is configured toreceive the message via the magnetic field using an on/off keyingcommunication protocol or via a separate communication channel, andwherein the separate communication channel comprises Bluetooth, Zigbeeor cellular network.
 20. The wireless power receiver of claim 17,wherein the controller is configured to cause the receive antenna toenable itself until the wireless power receiver is substantially fullycharged with the received power.
 21. The wireless power transmitter ofclaim 1, wherein the controller is configured to cause the firstreceiver device to enable itself differently than the second receiverdevice so that the amount of the power allocation received by the firstreceiver device is different than the amount of the power allocationreceived by the second receiver device.
 22. The method of claim 10,wherein the controller causes the first receiver device to enable itselfdifferently than the second receiver device so that the amount of thepower allocation received by the first receiver device is different thanthe amount of the power allocation received by the second receiverdevice.
 23. The wireless power receiver of claim 17, wherein thecontroller is configured to cause the receive antenna to enable itselfdifferently than receiver devices that are not disabled so that theamount of power received by the receive antenna is different than theamount of power received by the receiver devices that are not disabled.